Americans are so accustomed to President Trump upsetting the apple cart on the world stage that it can now seem surprising when a conference or summit goes smoothly.

That’s what happened this weekend in Buenos Aires, where Trump attended the annual Group of 20 summit of industrial nations. He presided over the signing of a new trade pact with Canada and Mexico and agreed to calm his burgeoning trade war with China. He offered pleasantries to world leaders he had previously attacked, shied away from headline-grabbing photo ops with controversial autocrats and signed onto the summit’s pro forma communique — something he conspicuously rejected at the G-7 summit earlier this year.

Negotiations over the communique saw American allies try to win over Trump: Condemnation of “protectionism” was left out of the document, and the United States was allowed to carve out a separate position on climate change, given Trump’s rejection of the Paris accords. Still, the White House’s assent in Argentina was cast a boon for the liberal order Trump has so often pilloried.

“The USA has approved a clear text on multi­lateralism that complies with international rules,” said French President Emmanuel Macron on Saturday. “They’ve approved a clear text on trade that has been discussed at length and is very clear on the reforms. They’ve approved a common text on energy matters, and this morning President Trump took the floor in the plenary session to say that even though he did not follow the Paris Accords he very much wanted to be involved in climate matters.”

Some analysts were less optimistic, viewing the muddled compromise as a sign of how Trump has made institutions like the G-20 all the more feeble. “The worry was that things could unravel, so there was a retraction of ambition from the other democratic leaders,” Thomas Wright of the Brookings Institution told The Post. “They are worried about him creating a fuss over attempts to forge cooperation, which means these summits now are just gatherings of the leaders without a real agenda. That’s the function of Trump.”

The weekend’s single most important event was a lengthy Saturday dinner between Trump and Chinese President Xi Jinping. It ended with a modest compromise: Trump agreed to at least delay a new round of tariffs on Chinese goods in return for additional Chinese purchases of American farm, energy and industrial goods. China’s concession was a White House attempt to chip away at Trump’s perennial gripe, the bilateral trade deficit with China.

But there’s little reason to think future talks will yield much progress on some of the thorniest sticking points between the two countries, including China’s practice of forced technology transfers from U.S. companies.

“The temporary cease-fire in the U.S.-China trade war left the toughest issues to future bargaining sessions, which will attempt to succeed where earlier efforts failed — and under an ambitious 90-day deadline,” explained my colleague David J. Lynch. “If the latest effort encounters the same roadblocks, Trump said he will proceed with his previous plan to raise tariffs on $200 billion in Chinese products to 25 percent from 10 percent, which was to have taken effect on Jan. 1.

The prospect of renewed trade hostilities by spring is all too real. The problem for Trump is that the United States is starting to experience the pain of his protectionist politics. “Across the country, thousands of small and medium-size businesses, farmers and retailers are also reportedly suffering financial losses as a result of higher prices for imported materials and goods and the ensuing foreign retaliatory measures,” noted an editorial in the Guardian.

The tensions are made all the more stark by the personal nature of the clash between Trump and Xi. “Both men have cast themselves as ‘maximum leaders,’ strong men defending the interests and honor of their nations,” said Aaron Friedberg, a former foreign policy adviser to former vice president Richard B. Cheney, to Lynch. “Neither wants to appear weak, which would seem to narrow the scope for compromise, but neither wants to be blamed for a complete breakdown in relations.”

But when faced with the presence of another “maximum leader” — Saudi Crown Prince Mohammed bin Salman — Trump demurred. The crown prince is currently reviled in the court of international public opinion for his alleged role in ordering the assassination of Saudi journalist Jamal Khashoggi. At the G-20, he was greeted with smiles and handshakes by some leaders, and stern lectures from others.

In neither instance was Trump at the head of the pack. In Washington, he has tried to shield Mohammed from accusations of direct complicity in Khashoggi’s murder and called on the preservation of U.S.-Saudi ties. But the G-20 summit exposed the limits of the president’s influence.

“His reputation has obviously been seriously damaged,” said José Miguel Vivanco, the executive director of Human Rights Watch’s Americas Division, of the Saudi crown prince. “I think he was convinced that he could walk on water and pay no cost. . . . But this case will follow him every time he leaves Saudi Arabia, probably for the rest of his life.”

On Sunday, a subdued Trump returned to Washington. While there was little rancor left in his wake, there was also little in the way of substance. “A president who prides himself on being the ultimate disrupter on the global stage,” noted my colleagues, “instead played the part of reluctant diplomat here in Argentina, at the risk of making himself something of a non-factor.” Given the precedents Trump himself has set, his critics may find that a welcome respite.